This invention relates to a wood preservative composition having an improved fixing ability in wood, process for treating wood with such wood preservative composition, and wood treated with such wood preservative composition.
It has been conventionally known that compositions containing a specified kind of metal compound or inorganic compound as a main component effectively serve as a wood preservative composition.
Metal compounds of these compositions include copper compounds such as copper acetate, chromium compounds such as copper chromate, potassium chromate, and sodium dichromate, and mercury compounds such as mercuric chloride.
Inorganic compounds of these compositions include arsenic compounds such as arsenious acid, fluorine compounds such as sodium fluoride, boron compounds such as boric acid and borax.
These compounds are mixed in a desired combination to obtain a wood preservative composition in the form of an aqueous solution. A fixing agent such as acetic acid and ammonia is often added to such an aqueous solution.
Then obtained composition is impregnated into wood to produce wood capable of preventing wood-attacking organisms from growing therein. These compositions originally have a wood preserving effect. The composition impregnated into wood is fixed in the wood through chemical reactions which take place between preservative components and between a preservative component and the wood. However, most of these compositions are poorly fixed in the wood and cannot maintain the wood preserving effect over a long period of time.
These compositions have other problems, too. For example, some of the components of these compositions, such as arsenic compounds, are fatally toxic and heavy metal compounds, such as chromium compounds and mercury compounds are considerably toxic. Accordingly, it is necessary to carefully handle these compositions when they are impregnated into wood so as not to risk workers' health, let alone to carefully prepare them. It is also necessary to carefully discard unnecessary pieces of wood treated with such a composition, which pieces are inevitably produced when the wood is cut into a desired form, and old wood products to prevent environmental pollution.
Reflecting the above problems, in recent years, attention has been turned to the use of an aqueous solution, as a wood preservative composition, containing as a main component copper borate or zinc borate in place of chromium compounds and arsenic compounds, and a volatile basic compounds. In these compositions, it has been known that the copper component has primarily a fungi resisting effect; the zinc component has primarily a fungi resisting effect and secondary insect resisting effect; and the boric acid component has primarily an insect resisting effect. Since neither chromium compounds nor arsenic compounds are used, these compositions have the advantage of having a low toxicity.
However, normally, compositions containing a boron compound as a main component cannot be fixed in the wood satisfactorily. It is said that, when the wood impregnated with such a composition is buried in the earth, 75 percent or more of the boric acid component of the boron compound will leach out in about two years.